Cyst nematodes are serious pests of many crops, and their extermination or control is an important agricultural problem. For example, soybean cyst nematode (SCN) is currently the most prevalent and consistently occurring pest of soybeans in the midwestern United States. At present, SCN is known to infest 64 of 99 Iowa counties and is suspected to be present in an additional 10 to 20 counties. Infestation causes dwarfing or stunting of roots, and stunting and yellowing of foliage. Soybean yield losses due to SCN can be as great as 50 to 75% when SCN densities are high or under drought conditions as occurred in parts of Iowa in 1988 through 1990. Current SCN management options include use of SCN-resistant soybean varieties and rotation with nonhost crops such as corn. See, G. L. Tylka et al., Soybean Cyst Nematode, Iowa State University Cooperative Extension Service, Publication PM-879 (1994).
A four-year rotation of nonhost, SCN-resistant soybean, nonhost, SCN-susceptible soybean is recommended to growers for fields with low SCN densities. Alternating use of SCN-resistant and SCN-susceptible soybeans is necessary to maintain the effectiveness of the soybean resistance. If SCN resistance is used continuously, the nematode adapts to the resistance and a race shift occurs. The aforementioned rotation can be effective at keeping low SCN densities from increasing, but is not very effective at reducing existing high densities of SCN. Unfortunately, many growers discover SCN infestations only after nematode densities have reached moderate to high densities. In such instances, growers are recommended to plant successive years of corn or some other SCN nonhost. However, growers often are unable to plant corn in the same field for several years in a row because of the limited corn acreage allowed by federal government programs, and there is not an economically viable third crop available for most growers in the upper Midwest.
In the early 1980s, T. Masamune et al., Nature, 297, 495 (1982), reported the extraction of a terpenoid called glycinoeclepin A from the roots of kidney bean plants and found that it stimulated hatch of SCN eggs at very low concentrations. The structure of this compound is shown below: ##STR2## Glycinoeclepin A can potentially be used to decrease SCN densities in infested soil if applied to fields during years when a nonhost crop, such as corn, is planted. SCN is an obligate parasite that must infect host soybean roots to live and multiply. SCN eggs "tricked" into hatching in the absence of a host soybean crop will die within days or weeks due to starvation, parasitism, or predation. Unfortunately, glycinoeclepin A is present in such small amounts in kidney bean roots that extraction of large quantities sufficient for application to agricultural fields is not possible. Since glycinoeclepin A was first identified, several research groups have successfully synthesized the compound or subunits thereof. For example, see E. J. Corey et al., J. Amer. Chem. Soc., 112, 8997 (1990); A. Miwa et al., Agricultural Biol. Chem., 51, 3459 (1987); K. Mori et al., Pure Appl. Chem., 61, 543 (1989) and G. A. Kraus et al., Agricultural Food Chem., 42, 1839 (1994). However, all of the prior synthetic routes are very complicated and, consequently, time-consuming and expensive to perform. Furthermore, these published synthetic routes result in the production of only micrograms or milligrams of the target compound. For practical agricultural application purposes, hundreds to thousands of grams of glycinoeclepin A will be needed. Therefore, them is a continuing need for compounds that can be used to control the timing of cyst nematode egg hatch.